MORB-derived amphibolites in the Paleozoic basement of the Aluminé Igneous-Metamorphic Complex, Neuquén, Argentina: Decoding its genesis, P-T evolution and pre-Andean regional correlations


  • I. Alejandra Urraza Departamento de Geología, Universidad Nacional del Sur San Juan 670, Bahía Blanca, Argentina.
  • S. Hugo Delpino INGEOSUR (CONICET-UNS) Alem 1253, Cuerpo B 1 piso. Oficina 110, Bahía Blanca, Argentina
  • L. Edith Grecco Departamento de Geología, Universidad Nacional del Sur San Juan 670, Bahía Blanca, Argentina.



MORB, Amphibolites, Thermobarometry, P-T path, Late Paleozoic, Triassic, Accretionary prism


Amphibolites included in the metapelitic sequence and as xenoliths in intrusive magmatic rocks outcropping in the southern sector of the Aluminé Igneous-Metamorphic Complex (AIMC), Neuquén, Argentina, are studied in detail in order to determine their origin and their subsequent metamorphic evolution. Field evidence and wholerock geochemistry indicate that these rocks were derived from a Mid-Ocean Ridge Basalt (MORB)-type protolith, and were accreted as tectonic slices into the metapelitic sequence that mainly formed the basal accretionary prism associated with a pre-Andean SW-NE subduction setting. Phase relationships, geochemistry of mineral assemblages and geothermobarometry indicate the presence of at least two metamorphic events (M1 1.9−3.9kbar, 677−745ºC and M2 6.4kbar, 723ºC) framed in a counterclockwise P-T path, comparable to those previously determined for the metapelitic country-rocks and metatroctolites outcropping in the same sector of the AIMC. Based on regional correlations and the agreement in the petrological, geochemical, geochronological and structural characteristics, we suggest that the MORB-derived Ñorquinco amphibolites and neighboring aluminous metasedimentary basement rocks of the AIMC belong to the eastern prolongation of the Western Series of the Coastal Accretionary Complex of Central Chile in west-central Argentina territory.


Anderson, J.L., Smith, D.R., 1995. The effects of temperature and fO2 on the Al-in-hornblende barometer. American Mineralogist, 80, 549-559.

Aguirre, L., Hervé, F., Godoy, E., 1972. Distribution of metamorphic facies in Chilean outline. Krystallinikum, 9, 7-19.

Boynton, N.V., 1984. Cosmochemistry of the rare earth elements: meteorite studies. In: Henderson, P. (ed.). Rare Earth Element Geochemistry. Development in Geochemistry, II Elsevier. 63-114.

Casquet, C., Baldo, E., Pankhurst, R.J., Rapela, C.W., Galindo, C., Fanning, C.M., Saavedra, J., 2001. Involvement of the Argentine Precordillera Terrane in the Famatinian mobile belt: geochronological (U-Pb SHRIMP) and metamorphic evidence from the Sierra de Pie de Palo. Geology, 29, 703-706.

Castro de Machuca, B., Perarnau, M., Alvarado, P., López, M.G., Sáez, M., 2012. A seismological and petrological crustal

model for the southwest of the Sierra de Pie de Palo, San Juan (Argentina). Revista de la Asociación Geológica Argentina, 69, 177-184.

Connolly, J.A.D., 1990. Multivariable phase diagrams; an algorithm based on generalized thermodynamics. American Journal of Science, 290, 666-718.

Creixell, C., Ortiz, M., Arévalo, C., 2012. Geología del área CarrizalilloEl Tofo, regiones de Atacama y Coquimbo. Mapa escala 1:100.000. Santiago, Carta Geológica de Chile, n°133-134, 82pp.

Dale, J., Holland, T., Powell, R., 2000. Hornblende - garnet - plagioclase thermobarometry: a natural assemblage calibration

of the thermodynamics of hornblende. Contribution to Mineralogy and Petrology, 140, 353-362.

Dale, J., Powell, R., White, R., Elmer, F., Holland, J., 2005. A thermodynamic model for Ca–Na clinoamphiboles in Na2O–CaO–FeO–MgO–Al2O3–SiO2–H2O–O for petrological calculations. Journal of Metamorphic Geology, 23, 771-791.

Deer, W., A., Howie, R.A., Zussman, J., 1966. An introduction to the rockforming minerals. London, Longmans, Green and Co. Ltd, 528pp.

Diener, J.F.A., Powell, R., White, R.W., Holland, T.J.B., 2007. A new thermodynamic model for clino and orthoamphiboles in the system Na2O–CaO–FeO–MgO–Al2O3–SiO2–H2O–O. Journal of Metamorphic Geology, 25, 631-65.

Duhart, P., McDonough, M., Muñoz, J., Martin, M., Villeneuve, M., 2001. El Complejo Metamórfico Bahía Mansa en la cordillera de la Costa del centro-sur de Chile (39º30’-42º00’S): geocronología K-Ar, 40Ar/39Ar y U-Pb e implicancias en la

evolución del margen sur-occidental de Gondwana. Revista geológica de Chile, 28(2), 179-208.

Ernst, W.G., Liou, J., 1998. Experimental phase equilibrium study of A1- and Ti-contents of calcic amphibole in MORB a semiquantitative thermometer. American Mineralogist, 83, 952-969.

Fuentes, P., Díaz Alvarado, J., Rodríguez, N., Fernández, C., Breitkreuz, C., Contreras A.A., 2018. Geochemistry, petrogenesis and tectonic significance of the volcanic rocks of the Las Tortolas Formation, Coastal Cordillera, northern Chile. Journal of South American Earth Sciences, 87, 66-86.

García-Sansegundo, J., Farias, P., Gallastegui, G., Giacosa, R.E., Heredia, N., 2009. Structure and metamorphism of the Gondwana basement in the Bariloche region (North Patagonian Argentine Andes). International Journal of Earth Sciences, 98, 1599-1608.

Gilbert, M.C., Helz, R.T., Poppand, R.K., Spear, F.S., 1982. Experimental studies of amphibole stability. In: Veblen, D.R., Ribbe, P.H. (eds.). Amphiboles: petrology and experimental phase relations. Washington, D.C, Mineralogical Society of America, pp 231–267.

Glodny, J., Lohrmann, J., Echtler, H., Gräfe, K., Seifert, W., Collao, S., Figueroa, O., 2005. Internal dynamics of a paleoaccretionary wedge: insights from combined isotope tectonochronology and sandbox modelling of the South-Central Chilean forearc. Earth and Planetary Science Letters, 231, 23-39.

Glodny, J., Echtler, H., Collao, S., Ardiles, M., Burón, P., Figueroa, O., 2008. Differential Late Paleozoic active margin evolution

in South-Central Chile (37ºS-40ºS) the Lanalhue Fault Zone. Journal of South American Earth Sciences, 26, 397-411.

Hawthorne, J.M., 1981. Stress relaxation behavior of biaxially oriented poly (ethylene terephthalate). Journal of Applier Polymer Science, 26(10), 3317-3324.

Heredia, N., García-Sansegundo, J., Gallastegui, G., Farias, P.E., Giacosa, R., Hogn, F., Tubia, J., Luis Alonso, J., Busquets, P., Charrier, R., Clariana, P., Colombo, F., Cuesta, A., Gallastegui, J., Giambiagi, L., González-Menéndez, L., Limarino, C., Martín-González, F., Pedreira, D., Cardo, R., 2018. Pre-Andean phases of construction of the Southern Andes basement in Neoproterozoic-Paleozoic times. In: Folguera, A., Contreras, E., Heredia, N., Encinas, A., Iannelli, S., Oliveros, V., Dávila, F.,

Collo, G., Giambiagi, L., Maksymowicz, A., Iglesia, P., Llanos, P., Turienzo, M., Naipauer, M., Orts, D., Litvak, V., Álvarez, O.,

Arriagada, C. (eds.). The Evolution of the Argentinian-Chilean Andes. Springer, 111-131. DOI: 10.1007/978-3-319-67774-3_5.

Hervé, F., 1987. Late Paleozoic subduction and accretion in Southern Chile. UNESCO, 11(3), 183-188.

Hervé, F., 1988. Late Palaeozoic subduction and accretion in Southern Chile. UNESCO, 11, 183-188.

Hervé, F., Faundez, V., Calderón, M., Massonne, H.J., Willner, A.P., 2007. Metamorphic and plutonic basement complexes. In: Moreno, T., Gibbons, W. (eds.). The Geology of Chile. London, the Geological Society, 5-19.

Hyppolito, T., Garcia-Casco, A., Juliani, C., Meira, V.T., Hall, C., 2014. Late Paleozoic onset of subduction and exhumation at the western margin of Gondwana (Chilenia Terrane): counterclockwise P-T paths and timing of metamorphism of deep-seated garnet-mica schist and amphibolite of Punta Sirena, Coastal Accretionary Complex. Lithos, 216-217, 409-434.

Hyppolito, T., Juliani, C., Garcia-Casco, A., Meira, V., Bustamante, A., Hall, C., 2015. LP/HT metamorphism as a temporal marker of change of deformation style within the Late Paleozoic accretionary wedge of central Chile. Journal of Metamorphic Geology, 33, 1003-1024.

Hyppolito, T., Angiboust, S., Juliani, C., Glodny, J., Garcia-Casco, A., Calderon, M., Chopin, C., 2016. Eclogite-, amphiboliteand blueschist-facies rocks from Diego de Almagro Island (Patagonia): Episodic accretion and Cretaceous thermal evolution of the Chilean subduction interface. Lithos, 264, 422-440.

Holland, T., Blundy, J., 1994. Non-ideal interactions in calcic amphiboles and their bearing on amphibole-plagioclase thermometry. Contribution to Mineralogy and Petrology, 116, 433-447.

Holland, T., Powell, R., 1998. An internally consistent thermodynamic data set for phases of petrological interest. Journal of Metamorphic Geology, 16(3), 309-343.

Johnson, M.C., Rutherford, M.J., 1989. Experimental calibration of the aluminium- in- hornblende geobarometer with application to Long Valley caldera (California). Geology, 17, 837-841.

Kato, T.T., 1985. Pre-Andean orogenesis in the Coast Ranges of central Chile. Geological Society of America Bulletin, 96, 918-924.

Kato, T.T., Sharp, W., Godoy, E., 2008. Inception of a Devonian subduction zone along the southwestern Gondwana margin:

Ar/39Ar dating of eclogite–amphibolite assemblage in blueschist boulders from the Coastal Range of Chile (41ºS). Canadian Journal of Earth Sciences, 45, 337-351.

Kato, T.T., Sharp, W.D., Godoy, E., 2009. Devonian-Carboniferous retro-eclogite (blueschist) boulders from the Cordillera de la Costa accretionary complex (41ºS), Chile: Tectonic similarities to high grade blueschists of the California Coast Ranges USA, Santiago, XII Congreso Geológico Chileno, 22-26.

Koppers, A.P., 2002. Ar/Ar CALC – software for 40Ar/39Ar age calculations. Computers and Geosciences, 28, 605-619.

Leake, B.E., 1964. The Chemical Distinction Between Ortho- and Para-amphibolites. Journal of Petrology, 5(2), 238-254.

Leake, B.E., Wooley, A.R., Arps, C.E.S, Birch, W.D.S., Birch, W.D, Gilbert, M.C., Grice, J.D., Hawthorne, F.C., Kato, A., Kisch, H.J., Krivivichev, V.G., Linthout, K., Laird, J., Mandarino, J.A., Maresch, W.V., Nickel, E.H, Tock, N.M.S, Schumacher, J.C, Smith, D.C, Stephenson, N.C.N., Ungaretti, L., Whittaker, E., Youzhi, G., 1997. Nomenclature of amphiboles: report of the subcommittee on amphiboles of International Mineralogical Association, Commission on New Minerals and Mineral Names. European Journal of Mineralogy, 9, 623-651.

Ludwig, K.R., 2003. Isoplot 3.09. A Geochronological Toolkit for Microsoft Excel. Berkeley Geochronology Center, 4 (Special

Publication), 70pp.

Martin, M., Kato, T., Rodríguez, C., Godoy, E., Duhart, P., McDonough, M., Campos, A., 1999. Evolution of Late Paleozoic accretionary complex and overlying forearcmagmatic arc south-central Chile (38-41ºS): constraints for the tectonic setting along the southwestern margin of Gondwana. Tectonics, 12(4), 582-605.

Martinez, J.C., Dristas, J.A., Massonne, H.J., 2011. Palaeozoic accretion of the microcontinent Chilenia, North Patagonian

Andes: high-pressure metamorphism and subsequent thermal relaxation. International Geology Review, 1, 1-19.

Martínez Dopico, C.I., 2008. Metamorphic P-T constraints for the low-temperature assemblages overimposed on metamorphic and igneous rocks nearby Ñorquinco Lake, Aluminé, NorthPatagonian Andes. Nice, 7th International Symposium on Andean Geodynamics, 319-321.

Massonne, H.J, Calderón, M., 2008. P-T evolution of metapelites from the Guarguaráz Complex, Argentina: evidence for

Devonian crustal thickening close to the western Gondwana margin. Revista Geológica de Chile, 35(2), 215-231.

Massonne, H.J., Willner, A.P., 2008. Phase relations and dehydration behavior of psammopelite and mid-ocean ridge basalt at verylow-grade to low-grade metamorphic conditions. European Journal of Mineralogy, 20, 867-879.

McDougall, I., Harrison, T.M., 1999. Geochronology and Thermochronology by the 40Ar/39Ar method. New York, Oxford University Press, 212pp.

Meschede, M., 1986. A method of discriminating between different types of mid-ocean ridge basalts and continental tholeiites with the Nb-Zr-Y diagram. Chemical Geology, 56, 207-218.

Misra, S.N., 1971. Chemical distinction of high-grade ortho and para-metabasites. Norsk Geologisk Tidsskr., 51, 311-316.

Newton, R.C., Haselton, H.T., 1981. Thermodynamics of the garnet-plagioclase-Al2SiO5-quartzgeobarometer. In: Newton, R.C., Navrotsky, A., Wood, B.J. (eds.). Advances in physical geochemistry. New York, Springer-Verlag, 1, 131-147.

Otten, M.T., 1984. The origin of brown hornblende in the Artfjallet gabbro and dolerites. Contribution to Mineralogy and Petrology, 86, 189-99.

Pankhurst, R.J., Rapela, C.W., 1998. The proto-Andean margin of Gondwana: an introduction. In: Pankhurst, R.J., Rapela, C.W. (eds.). The proto-Andean margin of Gondwana. London, Geological Society, 142 (Special Publications), 1-9.

Pankhurst, R.J., Rapela, C.W., Loske, W.P., Márquez, M., Fanning, C.M., 2003. Chronological study of the pre-Permian basement rocks of southern Patagonia. Journal of South American Earth Sciences, 16, 27-.44

Pearce, J.A., 1983. Role of sub-continental lithosphere in magma genesis at active continental margins. In: Hawkesworth, C.J., Norry, M.J. (eds). Continental Basalts and Mantle Xenoliths, Chesire, Shiva Publications, 203-249.

Pearce, J.A., Cann, J.R., 1973. Tectonic setting of basic volcanic rocks determined using trace element analyses. Earth Planetary Science Letter, 19, 290-300.

Raase, P., 1974. Al and Ti contents of hornblende, indicators of pressure and temperature of regional metamorphism. Contributions to Mineralogy and Petrology, 45, 231-236

Ramos, V.A., 1978. Estructura. Relatorio Geología y Recursos Naturales del Neuquén, 99-118.

Ramos, V.A, 1984. Patagonia: un continente paleozoico a la deriva? IX Congreso Geológico Argentino, 2 (Actas), 311-325.

Ramos, V.A., 1986. Tectonostratigraphy, as applied to analysis of South African Phanerozoic Basins by H. de la R. Winter,

discussion. Transactions Geological Society South Africa, 87(2), 169-179.

Ramos, V.A., 2000. Evolución tectónica de la Argentina. In: Caminos R. (ed.). Argentina, Instituto de Geología y recursos minerales, 29, 715-784.

Ramos, V.A., 2004. Cuyania, an Exotic Block to Gondwana: Review of a Historical Success and the Present Problems. Gondwana Research, 7(4), 1009-1026.

Rapela, C.W., 2000. The Sierras Pampeanas of Argentina: Paleozoic Building of the Southern Proto-Andes. In: Cordani U.G., Milani E.J., Thomaz-Filho A., Campos D.A (eds.). Tectonic Evolution of South America. 31st International Geological Congress, Río de Janeiro, 381-387.

Robinson, A.P., Spear, F.S., Schumacher, J.C., Laird, J., Klein, C., Evans, B.W., Doolan, B.L., 1982. Phase relations of metamorphic amphiboles: natural occurrence and theory. In: Veblen, D.R., Ribble, P.H. (eds.). Amphiboles: Petrology and Experimental Phase Relations. Mineralogical Society of America, Reviews in Mineralogy, 9B, 1-227.

Shaw, D.M., Kudo, A.M., 1965. A test of discriminant function in amphibolite problem. Mineralogical Magazine, 34, 423-435.

Spear, F.S., 1993. Metamorphic Phase Equilibria and Pressure–Temperature–Time Paths. Washington, Mineralogical Society

of America, 799pp.

Urraza, I.A., Grecco, L.E., Delpino, S.H., Arrese, M.L., 2006. Petrografía y estructura del sector norte del batolito de Aluminé, Neuquén, Argentina. San Luis (Argentina), 13º Reunión de Tectónica, Resúmenes, 61-62.

Urraza, I., Grecco, L., Delpino, S., Zentilli, M., 2008a. Magmatic and tectonic evolution of the Aluminé belt, Patagonian Batholith, Neuquen, Argentina. Québec (Canada), 2008 GACMAC-SEG-SGA Annual Meeting, May 26-28 2008, Session: GS4 - Igneous Petrology, Volcanology and Metamorphic Petrology, Abstracts, 174.

Urraza, I.A., Grecco, L.E., Delpino, S.H., Arrese, M.L., 2008b. Determination of rock ages by chemical analyses of Th, U, Pb in the mineral monazite (Ce, La, Th REE, U) PO4 using EPMA. Halifax, Nova Scotia, Canada, Annual General Meeting and Research Day, Institute for Research in Materials, Abstract, 36.

Urraza, I., Delpino, S., Grecco, L., Arrese, M., 2009. Petrografía, geotermobarometría y geocronología del basamento del

sector norte del Batolito Patagónico, Neuquén, Argentina. Río Cuarto. Argentina, Reunión de Tectónica, 14, Resúmenes, 34.

Urraza, I.A, Grecco, L.E., Delpino, S.H, Arrese, M.L, Rapela, C.W., 2011 Petrología y Estructura del Complejo ÍgneoMetamórfico Aluminé, Provincia del Neuquén, Argentina. Andean Geology, 38(1), 98-117.

Urraza, I.A., Delpino, S.H., Grecco, L.E, 2013. Presencia de Anfibolitas derivadas de MORB en el Basamento del Complejo Ígneo-Metamórfico Aluminé, Neuquén, Argentina. San Luis (Argentina), Simposio de Petrología Ígnea y Metalogénesis Asociada, Actas en Congreso, 95.

Urraza, I.A., 2014. Evolución magmática y tectonometamórfica del Complejo Ígneo- metamórfico Aluminé, Provincia de Neuquén, Argentina. Doctoral Thesis. Bahía Blanca (Argentina), Universidad Nacional del Sur, 206pp.

Urraza, I.A., Delpino, S.H., Grecco, L.E, 2015. Counterclockwise post-emplacement evolution of metatroctolites from Aluminé Igneous-Metamorphic Complex, Neuquén, Argentina. Andean Geology, 42(1), 36-55.

Vaughan, A.P.M., Pankhurst, R.J., 2008. Tectonic overview of the West Gondwana margin. Gondwana Research, 13, 150-162.

Whitney, D.L., Evans, B.W. 2010. Abbreviations for names of rockforming minerals. American Mineralogist, 95, 185-187.

Willner, A.P., Hervé, F., Thomson, S.N., Massonne, H.-J., 2004a. Converging PT-paths of Mesozoic HP-LT metamorphic units (Diego de Almagro Island, Southern Chile, 51º30’S): Evidence for juxtaposition during late shortening of anactive continental margin. Mineralogy and Petrology, 81, 43-84.

Willner, A.P., Glodny, J., Gerya, T.V., Godoy, E., Massonne, H., 2004b. A counterclockwise PTt path of high-pressure/lowtemperature rocks from the Coastal Cordillera accretionary complex of south-central Chile: constraints for the earliest stage of subduction mass flow. Lithos, 75, 283-310.

Willner, A. 2005. Pressure–Temperature Evolution of a Late Palaeozoic Paired Metamorphic Belt in North–Central Chile (34º–35º30’S). Journal of Petrology, 46(9), 1805-1833.

Willner, A.P., Thomson, S.N., Kröner, A., Wartho, J.A., Wijbrans, J., Hervé, F., 2005. Time markers for the evolution and exhumation history of a late Paleozoic paired metamorphic belt in central Chile (34º–35º30’S). Journal of Petrology, 46, 1835-1858.

Willner, A.P., Gerdes, A., Massonne, H.J., 2008. History of crustal growth and recycling at the Pacific convergent margin of

South America at latitudes 29-36ºS revealed by a U-Pb and Lu-Hf isotope study of detrital zircon from late Paleozoic accretionary systems. Chemical Geology, 253, 114-129.

Willner, A.P., Massone, H.J., Ring, U., Sudo, M., Thomson, S.N., 2011. P–T evolution and timing of a late Paleozoic fore-arc

system and its heterogeneous Mesozoic overprint in northcentral Chile (latitudes 31–32ºS). Geological Magazine, 149, 177-207.